Use Views to Partition External and Internal Information

acl internal {
  SUBNET ;
  localhost;
};
view "internal-view" {
  match-clients { internal; };
  zone "." IN {
    type hint;
    file "db.cache";
  };
  zone "internal.example.com " IN {
    ...
  };
};

view "external-view" {
  match-clients { any; };
  recursion no;
  zone "example.com " IN {
    ...
  };
};